Medical & Clinical

Understanding of the biological processes that control human and animal physiology can be difficult considering the moral implications that are involved in performing such studies. The use of stable isotope analysis provides a non-invasive approach with no adverse reactions which may be observed through using radioisotopes. The use of enriched isotope tracers with artificially high abundances of minor isotopes provides a relatively simple way of probing subtle biological processes.

Breath Analysis

After your subject has ingested an isotopically labelled meal (e.g. 13C-labelled glucose), exhaled CO2 from the patient will show enrichment in 13C levels relative to 12C. The time taken for the 13C isotope to appear in the exhaled breath gives some indication of the metabolic rate of the subject. Up to 220 breath samples can be analysed using our iso FLOW sample handling system for rapid analysis of large numbers of samples.

Body Fluid Analysis

Dosing a subject (human or animal) with doubly labelled water (e.g. water enriched in both deuterium and 18O) allows the total energy expenditure (TEE) of the subject to be determined. High performance deuterium and 18O isotope analysis of up to 180 saliva, blood and urine samples can be performed via headspace equilibration using the iso FLOW sample handling system.

Biochemical Analysis

To understand more about the complex physiological chemical processes that occur within the body, it is necessary to go beyond coarse breath and body fluid analysis. Our gas and liquid chromatography (GC-IRMS and LC-IRMS) systems are able to perform individual compound stable isotope analysis allowing you to find out more about these complex processes.

Medical publications using our instruments

Our customers use our instruments to do some amazing research in the medical application field. To show you how they perform their research and how they use our IRMS instruments, we have collected a range of peer-reviewed publications which cite our products. You can find the citations below and then follow the links to the publishing journal should you wish to download the publication.

If you would like to investigate our available citations in more detail, or email the citation list to yourself or your colleagues then take a look at our full citation database.

BACKGROUND: Exercise prevents the adverse effects of a high-fructose diet through mechanisms that remain unknown. OBJECTIVE: We assessed the hypothesis that exercise prevents fructose-induced increases in very-low-density lipoprotein (VLDL) triglycerides by decreasing the fructose conversion into glucose and VLDL-triglyceride and fructose carbon storage into hepatic glycogen and lipids. DESIGN: Eight healthy men were studied on 3 occasions after 4 d consuming a weight-maintenance, high-fructose diet. On the fifth day, the men ingested an oral (13)C-labeled fructose load (0.75 g/kg), and their total fructose oxidation ((13)CO2 production), fructose storage (fructose ingestion minus (13)C-fructose oxidation), fructose conversion into blood (13)C glucose (gluconeogenesis from fructose), blood VLDL-(13)C palmitate (a marker of hepatic de novo lipogenesis), and lactate concentrations were monitored over 7 postprandial h. On one occasion, participants remained lying down throughout the experiment [fructose treatment alone with no exercise condition (NoEx)], and on the other 2 occasions, they performed a 60-min exercise either 75 min before fructose ingestion [exercise, then fructose condition (ExFru)] or 90 min after fructose ingestion [fructose, then exercise condition (FruEx)]. RESULTS: Fructose oxidation was significantly (P < 0.001) higher in the FruEx (80% ± 3% of ingested fructose) than in the ExFru (46% ± 1%) and NoEx (49% ± 1%). Consequently, fructose storage was lower in the FruEx than in the other 2 conditions (P < 0.001). Fructose conversion into blood (13)C glucose, VLDL-(13)C palmitate, and postprandial plasma lactate concentrations was not significantly different between conditions. CONCLUSIONS: Compared with sedentary conditions, exercise performed immediately after fructose ingestion increases fructose oxidation and decreases fructose storage. In contrast, exercise performed before fructose ingestion does not significantly alter fructose oxidation and storage. In both conditions, exercise did not abolish fructose conversion into glucose or its incorporation into VLDL triglycerides. This trial was registered at clinicaltrials.gov as NCT01866215.

Determination of the safety of leucine supplementation in healthy elderly men.Amino acids (2016)

Leucine, a branched-chain amino acid (BCAA), has been shown to stimulate muscle protein synthesis, and thus has been proposed to prevent age-related muscle atrophy (sarcopenia). Therefore, leucine supplementation may have potential benefits in elderly populations to preserve muscle mass. The tolerable upper intake level (UL) for leucine intake in young men has recently been determined to be 500 mg kg(-1) day(-1), and increases in blood ammonia concentrations were seen at intake levels above 500 mg kg(-1) day(-1); the UL for leucine in elderly is unknown. The objective of the current study was to determine the safety of leucine supplementation in healthy elderly men. Six healthy elderly men (72.2 ± 3.5 years) received graded stepwise increases in leucine intakes ranging from 50 to 750 mg kg(-1) day(-1), on eight separate study days. Plasma and urinary biochemical variables, including blood ammonia, and an oral primed-continuous protocol of L-1-(13)C-Leucine was performed. Blood ammonia concentrations above normal values (35 µmol/L) were observed at leucine intakes >550 mg kg(-1) day(-1). Leucine oxidation measured as a F(13)CO2 (rate of label tracer oxidation) increased with increasing leucine intakes and started to plateau after 450 mg kg(-1) day(-1). Two-phased linear regression analysis of the F(13)CO2 data revealed a breakpoint of 431 mg kg(-1) day(-1) (R (2) = 0.73), suggesting that the upper limit to oxidize leucine was reached at that point. Taking the data together the upper limit for leucine intake in healthy elderly could be set similar to young men at 500 mg kg(-1) day(-1) or ~35 g/day for an individual weighing 70 kg.

Validity of body mass index in determining prevalence of overweight and obesity among Syrian late adolescents boysThe Social Science Journal (2016)

Mahfouz. Al-Bachir, Ibrahim Othman

Obesity is rising among adults and children worldwide, including populations living in developing countries. The published data related to Syria are insufficient to address this issue. Therefore, the aim of this study is to determine the prevalence of overweight and obesity, and to determine appropriate cut-off points of the body mass index (BMI) for defining overweight and obesity among Syrian adolescents. We record body weight (kg), height (m2), and body mass index (kg/m2). The total body fat mass (BFM) was determined by deuterium oxide dilution (DD). The total sample was used in a split-sample internal cross-validation. The BMI was integrated to multiple regressions and Bland and Altman's procedure was used to analyze the data. Receiver operating characteristics (ROC) curve was drawn to determine appropriate cut-off points of the BMI for defining overweight and obesity. The prevalence of overweight and obesity was 24.5% by BMI and 46.5% by body fat content. Receiver operating characteristics (ROC) curve analysis defined a BMI of 22.34kg/m2 as a cut-off for overweight with sensitivity of 84.0%, 80.9% specificity, and BMI of 24.71kg/m2 with 82.80% sensitivity and 93.0% specificity for obesity. The results of our study suggest lower BMI cut-offs for overweight and obesity in Syrian population than those of recommended by WHO.

During winter free living herbivores are often exposed to reduced energy supply at the same time that energy needs for thermoregulation increase. Several wild herbivores as well as robust horse breeds reduce their metabolism during times of low ambient temperature and food shortage. Thyroid hormones (TH) affect metabolic intensity and a positive effect of TH on basal metabolic rate (BMR) has been demonstrated in mammals and birds. As BMR and field metabolic rate (FMR) are often assumed to be intrinsically linked, TH may represent a reliable indicator for FMR. To test this hypothesis, ten Shetland pony mares were kept under semi-extensive central European conditions. During the winter month one group was fed 60% and one group 100% of their maintenance energy requirements. We measured FMR, locomotor activity, resting heart rate and TH levels in summer and winter. FMR, locomotor activity, resting heart rate and total T3 concentrations decreased substantially in winter compared to summer, whereas total T4 increased. Feed restriction led to a reduced FMR and resting heart rate, while TH and locomotor activity were not affected. Across both seasons FMR, resting heart and locomotor activity were positively correlated with total T3 but negatively and more weakly related with total T4.

Adaptation to a high protein diet progressively increases the postprandial accumulation of carbon skeletons from dietary amino acids in ratsAmerican Journal of Physiology - Regulatory, Integrative and Comparative Physiology (2016)

We aimed to determine whether oxidative pathways adapt to the overproduction of carbon skeletons resulting from the progressive activation of amino acid (AA) deamination and ureogenesis under a high protein (HP) diet. Ninety-four male Wistar rats, of which 54 were implanted with a permanent jugular catheter, were fed a normal protein diet for one week and were then switched to an HP diet for 1, 3, 6 or 14 days. On the experimental day, they were given their meal containing a mixture of 20 U-[15N]-[13C] AA, whose metabolic fate was followed for 4 h. Gastric emptying tended to be slower during the first 3 days of adaptation. 15N excretion in urine increased progressively during the first 6 days, reaching 29% of ingested protein. 13CO2 excretion was maximal as early as the first day, and represented only 16% of the ingested proteins. Consequently, the amount of carbon skeletons remaining in the metabolic pools 4 h after the meal ingestion progressively increased to 42% of the deaminated dietary AA after 6 days of HP diet. In contrast, 13C enrichment of plasma glucose tended to increase from 1 to 14 days of the HP diet. We conclude that there is no oxidative adaptation in the early postprandial period to an excess of carbon skeletons resulting from AA deamination in HP diets. This leads to an increase in the postprandial accumulation of carbon skeletons throughout the adaptation to an HP diet, which can contribute to the sustainable satiating effect of this diet.

Adaptation to a high protein diet progressively increases the postprandial accumulation of carbon skeletons from dietary amino acids in ratsAmerican Journal of Physiology - Regulatory, Integrative and Comparative Physiology (2016)

We aimed to determine whether oxidative pathways adapt to the overproduction of carbon skeletons resulting from the progressive activation of amino acid (AA) deamination and ureogenesis under a high protein (HP) diet. Ninety-four male Wistar rats, of which 54 were implanted with a permanent jugular catheter, were fed a normal protein diet for one week and were then switched to an HP diet for 1, 3, 6 or 14 days. On the experimental day, they were given their meal containing a mixture of 20 U-[15N]-[13C] AA, whose metabolic fate was followed for 4 h. Gastric emptying tended to be slower during the first 3 days of adaptation. 15N excretion in urine increased progressively during the first 6 days, reaching 29% of ingested protein. 13CO2 excretion was maximal as early as the first day, and represented only 16% of the ingested proteins. Consequently, the amount of carbon skeletons remaining in the metabolic pools 4 h after the meal ingestion progressively increased to 42% of the deaminated dietary AA after 6 days of HP diet. In contrast, 13C enrichment of plasma glucose tended to increase from 1 to 14 days of the HP diet. We conclude that there is no oxidative adaptation in the early postprandial period to an excess of carbon skeletons resulting from AA deamination in HP diets. This leads to an increase in the postprandial accumulation of carbon skeletons throughout the adaptation to an HP diet, which can contribute to the sustainable satiating effect of this diet.

Minimally invasive 13C-breath test to examine phenylalanine metabolism in children with phenylketonuriaMolecular Genetics and Metabolism (2015)

Background Phenylketonuria (PKU) is an autosomal recessive disorder caused by deficiency of hepatic phenylalanine hydroxylase (PAH) leading to increased levels of phenylalanine in the plasma. Phenylalanine levels and phenylalanine hydroxylase (PAH) activity monitoring are currently limited to conventional blood dot testing. 1-13C-phenylalanine, a stable isotope can be used to examine phenylalanine metabolism, as the conversion of phenylalanine to tyrosine occurs in vivo via PAH and subsequently releases the carboxyl labeled 13C as 13CO2 in breath. Objective Our objective was to examine phenylalanine metabolism in children with PKU using a minimally-invasive 1-13C-phenylalanine breath test (13C-PBT). Design Nine children (7 M: 2 F, mean age 12.5 ± 2.87 y) with PKU participated in the study twice: once before and once after sapropterin supplementation. Children were provided 6 mg/kg oral dose of 1-13C-phenylalanine and breath samples were collected at 20 min intervals for a period of 2 h. Rate of CO2 production was measured at 60 min post-oral dose using indirect calorimetry. The percentage of 1-13C-phenylalanine exhaled as 13CO2 was measured over a 2 h period. Prior to studying children with PKU, we tested the study protocol in healthy children (n = 6; 4 M: 2 F, mean age 10.2 ± 2.48 y) as proof of principle. Results Production of a peak enrichment (Cmax) of 13CO2 (% of dose) in all healthy children occurred at 20 min ranging from 17–29% of dose, with a subsequent return to ~5% by the end of 2 h. Production of 13CO2 from 1-13C-phenylalanine in all children with PKU prior to sapropterin treatment remained low. Following sapropterin supplementation for a week, production of 13CO2 significantly increased in five children with a subsequent decline in blood phenylalanine levels, suggesting improved PAH activity. Sapropterin treatment was not effective in three children whose 13CO2 production remained unchanged, and did not show a reduction in blood phenylalanine levels and improvement in dietary phenylalanine tolerance. Conclusions Our study shows that the 13C-PBT can be a minimally invasive, safe and reliable measure to examine phenylalanine metabolism in children with phenylketonuria. The breath data are corroborated by blood phenylalanine levels in children who had increased responses in 13CO2 production, as reviewed post-hoc from clinical charts.

Plasma glucose kinetics and response of insulin and GIP following a cereal breakfast in female subjects: effect of starch digestibility.European journal of clinical nutrition (2015)

BACKGROUND/OBJECTIVES: Foods with high contents of slowly digestible starch (SDS) elicit lower glycemic responses than foods with low contents of SDS but there has been debate on the underlying changes in plasma glucose kinetics, that is, respective contributions of the increase in the rates of appearance and disappearance of plasma glucose (RaT and RdT), and of the increase in the rate of appearance of exogenous glucose (RaE) and decrease in endogenous glucose production (EGP).\n\nSUBJECTS/METHODS: Sixteen young healthy females ingested in random order four types of breakfasts: an extruded cereal (0.3% SDS: Lo-SDS breakfast) or one of three biscuits (39-45% SDS: Hi-SDS breakfasts). The flour in the cereal products was labeled with (13)C, and plasma glucose kinetics were measured using [6,6-(2)H2]glucose infusion, along with the response of plasma glucose, insulin and glucose-dependent insulinotropic peptide (GIP) concentrations.\n\nRESULTS: When compared with the Lo-SDS breakfast, after the three Hi-SDS breakfasts, excursions in plasma glucose, the response of RaE, RaT and RdT, and the reduction in EGP were significantly lower (P<0.05). The amount of exogenous glucose absorbed over the 4.5-h postprandial period was also significantly lower by ~31% (P<0.001). These differences were associated with lower responses of GIP and insulin concentrations.\n\nCONCLUSIONS: Substituting extruded cereals with biscuits slows down the availability of glucose from the breakfast and its appearance in peripheral circulation, blunts the changes in plasma glucose kinetics and homeostasis, reduces excursions in plasma glucose, and possibly distributes the glucose ingested over a longer period following the meal.European Journal of Clinical Nutrition advance online publication, 8 April 2015; doi:10.1038/ejcn.2015.50.

RATIONALE: Natural stable carbon (δ(13)C) and nitrogen isotope ratios (δ(15)N) of humans are related to individual dietary habits and environmental and physiological factors. In forensic science the stable isotope ratios of human remains such as hair and nail are used for geographical allocation. Thus, knowledge of the global spatial distribution of human δ(13)C and δ(15)N values is an essential component in the interpretation of stable isotope analytical results. METHODS: No substantial global datasets of human stable isotope ratios are currently available, although the amount of available (published) data has increased within recent years. We have herein summarised the published data on human global δ(13)C andδ(15)N values (around 3600 samples) and added experimental values of more than 400 additional worldwide human hair and nail samples. In order to summarise isotope ratios for hair and nail samples correction factors were determined. RESULTS: The current available dataset of human stable isotope ratios is biased towards Europe and North America with only limited data for countries in Africa, Central and South America and Southeast Asia. The global spatial distribution of carbon isotopes is related to latitude and supports the fact that human δ(13)C values are dominated by the amount of C4 plants in the diet, either due to direct ingestion as plant food, or by its use as animal feed. In contrast, the global spatial distribution of human δ(15)N values is apparently not exclusively related to the amount of fish or meat ingested, but also to environmental factors that influence agricultural production. CONCLUSIONS: There are still a large proportion of countries, especially in Africa, where there are no available data for human carbon and nitrogen isotope ratios. Although the interpretation of modern human carbon isotope ratios at the global scale is quite possible, and correlates with the latitude, the potential influences of extrinsic and/or intrinsic factors on human nitrogen isotope ratios have to be taken into consideration.

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